Method and apparatus for continuously maintaining a layer of coating material on a screen during printing and for controlling the viscosity of the coating material



May 24 1966 J. A. BLACK BESZ MI NETHOD AND APPARATUS FOR CONTINUOUSLY MAINTAINING A LAYER OF COATING MATERIAL ON A SCREEN DURING PRINTING AND CONTROLLING THE VISCOSITY OF THE COATING MATERIAL Filed fiepm 22 1964 J 2'5" 2 4g 29 I M 30 IL 11/ /a a 28 r M IIUQLI- .w 4 /9 INVENTOR. 1/14/45? 3146/6 ATTORNEYS United States Patent METHOD AND APPARATUS FOR CQNTHNUOUSLY MAINTAINING A LAYER 0F CGATING MATE- REAL ON A SCREEN DURING PRINTING AND FUR CONTROLLENG THE VISCOSITY OF THE COATING MATERIAL James A. Black, 13700 Sparta NW., Kent, Mich. Filed Sept. 22, 1964, Ser. No. 398,236 Claims. (Cl. 101-124) This is a continuation-impart of my copending application Serial No. 199,970, which was filed June 4, 1962, and is now abandoned.

The present invention relates to screen stencilling methods and machines by means of which coating ma-' terials such as pigmented inks, adhesives and functional deposits may be forced through a screen stencil onto sheets of paper or other stock for making posters, decalcomania or other products, incorporating graphic design, functional deposits and coatings.

Former screen stencilling processes and machines, which utilized the processes such as, for example, those disclosed in my Us. Letters Patent No. 2,606,492, had certain limitations in their use. For example, quick drying ink and coating materials could not be used, due to the fact that the material was spread out over the open stencil for extended periods during which the solvent progressively evaporated from the material and it became thickened, or heavy. (See FIGS. 6 and 7 of said Patent No. 2,606,492 for illustrations of this.) Even with slow drying materials, the solvents evaporated relatively rapidly and the machine had to be stopped frequently to recondition the coating material in the stencil irame and regain the quality of print.

Furthermore, the prints made by such former processes lacked uniformity in color intensity and gradations occurred between smooth and rough texture printing due to the fact that some prints were made with thin coating material and others were made with relatively thick material. Slow drying coatings were one of the partial answers which those in the art provided to keep the printing of good quality. Another limitation in the use of such former machines was that the printed sheets, being coated with slow drying material, had to be kept separate during the drying process so that they would not stick together, or the printed impressions thereon be spoiled by contact of one printed sheet with another. necessitated either storing the sheets in racks by hand or the use of complicated drying machines for keeping the sheets separated while drying.

The present invention overcomes the above limitation and makes possible the use of quick-drying coating materials so that the sheets can be piled one upon another immediately after the screening of them. Also, the present invention provides for constant control of the viscosity and the solvent content of the coating materials being used. Therefore, screen prints made by the present process are all of uniform color intensity. This is accomplished by continuously recirculating the coating material through an external viscosity control device while the machine continues in operation. Such a viscosity control is especially important with ceramic, transparent, and halftone printing inks.

When the openings in the stencil are small and ink This 3 ,252 Al l Patented May 24, 1966 usage through the screen is very little, the ink in the screen will lose sufiicient solvent to become heavy, thus causing a serious variation in color and solids deposit. In a viscosity control system the lost solvent is constantly replaced and the solvent con-tent of each print is the same. This means that all sheets, or prints, will have the same drying time. the use of higher speed screen presses which produce more printed sheets per hour and eliminates the usual down time of presses necessary to recondition the coating material or ink in the stencil frame. Another limitation on former cylinder presses of the type shown in my Patent No. 2,606,492 was that when the squeegee was raised off contact with the screen and the flow-coated blade applied ink to the screen stencil on the return stroke (as illustrated in FlIG. 6 of said patent), the pressure of the ink depressed the slightly elevated screen. As a result of this, the coated material in the stencil frame was distributed more heavily in the middle of the screen than at the sides, due to the fact that the center of the screen is resilient and unsupported against pressure. Thus, when each successive portion of the screen reached the cylinder (where it was supported in perfect horizontal line contact) the film of coating material on the screen crowned in the middle and a heavier deposit of material was laid in the middle of the stock being processed than was laid at the sides, where the screen stencil is attached and supported. This resulted in a non-uniform coating of each individual sheet of stock processed. As will be amply shown, in the present invention the stencil is flow-coated immediately after and adjacent to the print-01f and is, therefore, supported by the cylinder, thus no depressed crown or coating is effected.

Another. limitation inherent in former processes and machines was that after the print-off of coating material from the stencil screen onto the stock, the screen was left almost, but not quite, dry (see left-hand end of stencil screen shown in FIG. 6 of Patent No. 2,606,492). As a result of this, the small amount of coating material remaining in the screen tended to dry out relatively rapidly, thus leaving minute quantities of dried materials in the open portions of the stencil mesh which would eventually accumulate to clog the open portions and spoil the print. The present invention provides for flow-coating the screen with coating material immediately after the print-0d and in close proximity to the cylinder and the squeegee so that substantially all of the screen is coated with a relatively heavy layer of coating material at all times, thus preventing any drying out of coating material in the open mesh of the stencil. Another advantage is that in flow coating immediately after and adjacent to the squeegee and cylinder, the time lapse of ink layer on the stencil is progressively the same, where-as in the older system flow coating was done on the return stroke. Thus, the beginning of the flow coat had a greater time to seep into the stencil and displace air in the mesh and this portion of the stencil consequently produced a more solid print in the finish of the print-oil stroke. This is very noticeable in transparent and ceramic colors. A still further advantage of the present invention lies in a provision for continuously removing the coating material from the stencil frame for reconditioning, thus eliminating any pile up of material within the stencil frame and making possible the use of a shorter The invention makes possible 3 screen and screen frame (again see FIG. 6 of Patent No. 2,606,492), thus enabling a shorter stroke of the machine, faster operation and increased-production.

The invention also provides a method for screen stencilling onto continuous web stock as well as onto the sheet stock to which earlier methods and machines were limited.

The new method and apparatus for performing it are illustrated diagrammatically in the accompanying drawing, wherein:

FIG. 1 is a sectional view illustrating screen stencilling apparatus in the printing phase of operation for screen printing onto sheet stock;

FIG. 2 is a similar sectional view illustrating the nonprinting phase of operation;

FIG. 3 illustrates the application of the new method in the screen printing of continuous web stock; and

FIG. 4 is an enlarged sectional view which illustrates certain aspects of the apparatus of the previous figures in greater detail.

For clarity of presentation, certain mechanical details have been omited from the drawings, but these may be said to be generally similar in character to details shown in my Patent No. 2,606,492, and FIGS. 1 and 2 of the present drawing compare with FIGS. 6 and 7 of that patent by way of contrasting the new mode of operation with the former mode. Referring then in detail to FIGS.

1 and 2, a stock-supporting cylinder 9 is mounted for I reciprocating rotary movement through print and nonprint strokes, the print stroke being in a counter-clockwise direction as indicated in FIG. 1, and the non-print stroke being in a clockwise direction as indicated in FIG. 2. Sheet stock, designated 10, is fed to the cylinder 9 over a feedboard indicated at 11 for processing at the print-ofi station at the top of the cylinder, and after it has been processed the stock is carried away from the cylinder over a delivery board indicated at 12.

A screen stencil 13 of fine mesh silk or wire secured to the underside of a stencil frame 14, is mounted above the cylinder 9 for reciprocating linear movement through forward print strokes as indicated in FIG. 1 and through non-print return strokes as indicate in FIG. 2. The screen stencil 13 is also mounted for reciprocating vertical displacement toward the cylinder 9 at the beginning of the print stroke and away from the cylinder 9 at the end of the print stroke.

A combination squeegee and flow-coater assembly generally designated 15, is mounted above the screen stencil 13 for vertical reciprocating movements toward the stencil 13 and cylinder 9 at the beginning of each print stroke and away from the stencil and cylinder at the end of each print stroke. This combination squeegee and flow-coater 15, which is shown in detail in FIG. 4, comprises a fountain flow-coat reservoir 16 having a rubber or plastic spreader blade 17 at its lower end, and a take-up reservoir,

18 having a rubber or plastic squeegee blade 19 at its lower end.

A composite viscosity control and recirculating device is indicated at 20, by which coating material is continuously and automatically recirculated from the take-up reservoir 18 of flow-coater 15 to the reservoir 16 thereof. The device 20 includes a hydraulic pump means which is driven by a motor 26 in a known manner and an automatic viscosity control apparatus 27 of the nature disclosed in US. Patent Nos. 2,254,575 and 2,773,507. Pump 25 operates to draw excess coating material from take-up reservoir 18 through a take-up conduit 21. This material is then pumped into the viscosity control 27, where it is automatically tested for viscosity and reconditioned by the addtion of needed amounts of new solvent material, supplied through a solvent supply conduit 22. The reconditioned coating material is then returned to the flow-coat reservoir 16 through a delivery conduit 23. As best seen in FIG. 4, the fountain flow-coater 15 has a gate means 24 at the lower end of reservoir 16 which operates to close this reservoir when the gate means is in its upper position and to open the reservoir when it is in its lower postion. The open (lower) position is shown by the solid lines in the figure, and the closed (upper) position is shown in phantom. Gate 24 is moved from one of its positions to the other by an actuating lever 28 which is pivotally supported at 29, where it passes through the outer wall of the fiow-coater structure. The inner end of lever 28 is loosely coupled with the gate 24, while the outer end of the lever is loosely coupled to a fixed external pivot point 30. Thus, upward movement of the fiow-coater 15 causes the inner end of the lever to be raised, which in turn raises gate 24 and closes reservoir 16. Conversely, downward movement of the flow-coater lower the inner end of the actuating lever, thereby lowering the gate and opening the reservoir.

0perati0n-FIGURES 1 and 2 Sheets of stock 10 are intermittently fed to the stocksupporting cylinder 9 over the feedboard 11 at the beginning of each print stroke, and removed after the print-off over delivery board 12. Conventional conveyor tapes, not shown, may be associated with the feed-board 11 and delivery board 12, and suitable grippers and strippers such as those shown in Patent No. 2,606,492 may be associated with the cylinder 9. As each sheet 10 is fed to the print-off station at the top of the cylinder 9, the stencil screen 13 is lowered into contact with the sheet 10, and the squeegee and flow-coater assembly 15 is lowered so that the squeegee blad 19 contacts the screen 13 to effect tangential line contact between the sqeegee blade 19, screen 13, stock 10 and cylinder 9. Further, lowering of the flow-coater 15 serves to open gate 24 and reservoir 16, in the manner previously described.

During the print stroke, cylinder 9 rotates counterclockwise, and the screen stencil 13 and stock sheet 10 together move simultaneously to the left as seen in FIG. 1. As the flow-coaters lower gate 25 is open during the print stroke, the left-hand portion of the screen is progressively recoated with an even layer of coating material from reservoir 16 closely following and concurrently with the print-off. Also, the excess of coating material on the right-hand portion of the screen is wiped off by squeegee 19 and progressively taken up through the take-up conduit 21 by pump 25. This excess coating material is then fed into the viscosity control device 27, where it is automatically recirculated and reconditioned with solvent material as required. Finally, the reconditioned solvent is returned to the flow-coat reservoir 16 through the delivery conduit 23 by the viscosity control device.

At the end of the print stroke, the screen stencil 13 is moved upwardly a short distance away from the cylinder 9. Squeegee 19 and flow-coater assembly 15 are moved farther upwardly and away from both the cylinder 9 and the screen stencil 13, as illustrated in FIG. 2, thereby closing gate 24 and preventing any further coating material from leaving reservoir 16. The screen stencil is then returned through its non-print stroke to the right (FIG. 2) to its starting position, while the cylinder 9 is simultaneously moved clockwise to its startin position.

Operation-FIGURE 3 FIG. 3 illustrates the screen printing of continuous web stock 10a, such as wall paper, wrapping paper, upholstery covering materials and the like. In this application of the invention, the mode of operation is generally the same as that previously described, except that the cylinder 9a always moves in the same (counter-clockwise) direction with an intermittent motion which advances the web to the left during the print-off and halts the movement of the web during the non-print stroke of the stencil. By proper coordination of the movements of the various parts of the apparatus, each successive printing on the web material can be made to register perfectly with the preceding printing, and the impressions on the web material are all, of the same color intensity by reason of the constant viscosity control of the coating material used.

It will thus be seen that the invention provides a method and apparatus for screen stencil printing which possesses many advantages over former methods and machines, and while but two applications and embodiments of the invention have been herein shown and described, it will be understood that the invention comprehends all such modifications thereof as fall within the scope of the following claims.

I claim:

1. A screen stencilling method comprising the steps of coating one side of a stencil screen from end to end with a layer of coating material, progressively printing off at least some of said coating material through said screen and onto stock positioned adjacent the other side of the screen, and progressively recoating said one side of the screen from end to end with another layer of coating material during said printing-off such that substantially all of said one side of the screen is coated with a layer of coating material at all times during the repetition of said steps.

2. A screen stencilling method according to claim 1 including the additional steps of removing from said screen during the said print-ofi step substantially all of said coating material in excess of that actually printed olf, reconditioning removed coating material having altered characteristics due to exposure to a controlled viscosity, and recoating said one side of the screen with said reconditioned coating material.

3. A screen stencilling method comprising the steps of feeding stock over a rotatably mounted cylinder, moving a fiat stencil screen into contact with the cylinder-supported part of said stock, moving a squeegee into contact with the stencil screen along the screens line of tangency with the cylinder-supported stock and at the same time moving a fountain flow-coater into flow-coating position relative to the screen and in close proximity to said squeegee, imparting rotary movement to said cylinder and linear movement to said stencil whereby the squeegee progressively prints off coating material through the screen and onto said stock while concurrently therewith the fountain flow-coater progressively recoats the stencil screen, whereby substantially all of said screen is coated with a layer of coating material at all times during the repetition of said steps.

4. A screen stencilling method according to claim 3 including the additional steps of moving the stencil away from the cylinder and moving the squeegee and the fountain flow-coater away from the cylinder and the stencil at the conclusion of the print-off, and then returning the stencil to its starting position.

5. A screen stencilling method according to claim 3 including the additional steps of removing excess coating material from the screen during the print-off, recirculating said excess material through a viscosity control device for reconditioning, and then returning the reconditioned material to said fountain flow-coater.

6. Screen stencilling apparatus comprising a stocksupport and a screen stencil adjacent said stock-support, a squeegee means adjacent the stencil movable relative thereto for printing off coating material through the stencil and onto stock supported on said stock-support, means for taking up from said stencil coating material in excess of that printed off through said stencil and which accumulates in front of the said squeegee means, means operatively associated with said taking-up means for reconditioning the said coating material'which has been taken up by adjusting its viscosity to a predetermined value, and means for recoating said screen stencil with said reconditioned coating material in close proximity to said squeegee means during the said printing off.

7. Screen stencilling apparatus comprising a rotatable stock-supporting cylinder, a stencil means having a generally flat screen stencil mounted above said cylinder for forward and returning reciprocating linear movements relative to the cylinder through print and non-print strokes,

said stencil means providing reciprocating vertical displacement of said screen stencil toward and away from said cylinder, a squeegee means having a generally flat squeegee blade mounted for vertical reciprocating movements toward and away from the cylinder, said stencil means and said squeegee means arranged such that at the beginning of the said forward screen stencil movement the screen stencil and the squeegee blade are moved into tangential line contact with stock positioned upon and supported by said cylinder to print off coating material through said screen stencil and onto said stock, and said stencil means and squeegee means arranged such that said screen stencil and squeegee blade are moved out of contact with the cylinder-supported stock at the end of I said forward screen stencil movement, and means for continuously depositing coating material upon said screen stencil in proximity with said squeegee and on that portion of said screen stencil already printed off by said squeegee as said screen stencil moves under said squeegee during its said forward print-stroke, such that said printed-off portion of said stencil is continuously coated with said coating material.

8. Screen stencilling apparatus comprising a rotatable stock-supporting cylinder, a stencil means having a generally flat screen stencil mounted above said cylinder for forward and returning reciprocating linear movements relative to the cylinder through print and non-print strokes, said stencil means providing reciprocating ver tical displacement of said screen stencil toward and away from said cylinder, a squeegee means having a generally flat squeegee blade mounted for vertical reciprocating movements toward and away from the cylinder, said stencil means and said squeegee means arranged such that at the beginning of said forward screen stencil movement the screen stencil and the squeegee blade are moved into tangential line contact with stock positioned upon and supported 'by said cylinder to print off coating material through said screen stencil and onto said stock and said stencil means and squeegee means arranged such that said stencil and squeegee blade are moved out of contact with the cylinder-supported stock at the end of said forward screen stencil movement, and viscosity control means for taking up coating material in excess of that printed off through said screen stencil which accumulates adjacent said squeegee as said screen stencil moves thereunder, said viscosity control means reconditioning the coating material which has been taken up to a preselected viscosity and said viscosity control means continuously recoating said screen stencil with reconditioned coating material in close proximity to said squeegee blade during said print stroke.

9. Screen stencilling apparatus comprising: a rotatable stock-supporting cylinder; a stencil means having a fiat screen stencil mounted above said cylinder for forward and returning reciprocating linear movements relative to the cylinder through print and non-print strokes; said stencil means providing reciprocating vertical displacement of said screen stencil toward and away from said cylinder; at squeegee and flow-coater assembly, including a squeegee blade, a take-up reservoir positioned in advance of said blade, and a fountain flow-coater reservoir with a spreader blade rearwardly thereof; means mounting said squeegee and flow-coater assembly for vertical reciprocating movements toward and away from the cylinder and the said screen stencil such that at the beginning of the 7 8 away from said cylinder and screen stencil upon the com- References Cited by the Examiner pletion of said print stroke. UNITED STATES ATENTS 10. Screen stencilling apparatus according to claim 9 2157 638 5/1939 Soubier 101 115 including viscosity control means; said means taking p 2382920 8/1945 s h f 101 120 coating material in excess of that printed off through 5 2571064 10/1951 S h f 01.420 said screen stencil which has, accumulated in said take-up 2:606:492 3/1952 Black 101 124 reservoir, reconditioning said coating material to a preselected viscosity, and returning the reconditioned coating ROBERT E. PULFREY, Primary Examiner. material to sand fountain fiow-coater reservoir. 10 WILLIAM PENN Examiner 

1. A SCREEN STENCILLING METHOD COMPRISING THE STEPS OF COATING ONE SIDE OF A STENCIL SCREEN FROM END TO END WITH A LAYER OF COATING MATERIAL, PROGRESSIVELY PRINTING OFF AT LEAST SOME OF SAID COATING MATERIAL THROUGH SAID SCREEN AND ONTO STOCK POSITIONED ADJACENT THE OTHER SIDE OF THE SCREEN, AND PROGRESSIVELY RECOATING SAID ONE SIDE OF THE SCREEN FROM END TO END WITH ANOTHER LAYER OF COATING MATERIAL DURING SAID PRINTING-OFF SUCH THAT SUBSTANTIALLY ALL OF SAID ONE SIDE OF THE SCREEN IS COATED WITH A LAYER OF COATING MATERIAL AT ALL TIMES DURING THE REPETITION OF SAID STEPS. 